The recent advance of the semiconductor fabrication technology has made it possible to construct ultra-fine structures of the micrometer order. Triggered by the advanced processing technology, efforts are being made on the research and development of so-called micro-machines. The actuator which is one of elemental devices of the micro-machine is of great concern.
From the movement aspect, the microactuator is generally divided into rotary and direct-acting types. Since the direct-acting type has a very simple structure, most research works address direct-acting actuators. From the driving principle, the microactuator is generally divided into electrostatic, piezoelectric, electromagnetic, shape-memory alloy, photo-drive, and pneumatic drive modes. Of these, the electrostatic mode is most attractive, and the piezoelectric mode next. The electromagnetic mode actuator is considered in itself to be one of most attractive actuators because high efficiency and high output are expected from its principle, and they have been utilized in the prior art motor technology. Nevertheless, there are few research reports relating to direct-acting microactuators of the electromagnetic mode. One main reason is the difficulty of size reduction due to complex structure.
Components of the electromagnetic direct-acting microactuator include a permanent magnet and a coil. With respect to the permanent magnet, magnet materials exhibiting high performance despite small size have been developed by virtue of the advanced thin-film or miniaturization technology. As to the coil, small size coils have been developed as a result of the progress of micro-electromechanical systems utilizing the semiconductor micropatterning technology.
A voice coil motor is one of the linear drive electromagnetic actuators which have been widely used. When a drive system is assembled using a voice coil motor, an operating or rotor section is generally provided with a linear guide for preventing the operating section from deviating from the drive direction. The linear guide has a guide rail and a slider which are movably combined via a bearing. The slider can serve as a rotor. Among linear guides using ball bearings, linear guides having a slider with plane dimensions of at least 3 mm×6 mm are now commercially available. The guide rail used therein has a size which is the sum of the size of the slider, the stroke, and the size of an attachment to a stationary section (stator). Despite a need for driving to the sub-millimeter order, the actuator has a size of 1 cm or larger. A pneumatic bearing is of the design that a rod-shaped slider is movably inserted into an axial through-hole in a quadrangular prism or cylindrical guide rail. This design further increases the size of the actuator since the guide rail should have a sufficient length relative to the diameter of the rod-shaped slider so as to prevent the slider from becoming loose in the guide rail.
As understood from the above discussion, it is concluded that the presence of a relatively large size linear guide in the actuator accounts for the difficulty of size reduction of electromagnetic direct-acting actuators.
The references pertinent to the technology of the present invention include Wakiwaka et al., Journal of the Magnetics Society of Japan, Vol. 24, No. 4-2 (2000), pp. 955-958; and Wakiwaka et al., Proceedings of the 25th Annual Conference on Magnetics in Japan, 2001, p. 302.